The present invention is directed to the preparation of, and coating compositions which are water-dilutable upon neutralization with acids. The coating compositions are electrically depositable at the cathode of an electrodeposition system and will crosslink through thermal polymerization.
Electrodeposition of synthetic resins and plastics, although known for substantial time, has gained technical importance as a coating process is only recent years. The coating compositions or binders primarily used for commercial electrodeposition contain polycarboxylic acid resins neutralized with bases. The products deposit at the anode of an electrodeposition system. Owing to the acidic character of the resins, they are sensitive to corroding influences exerted by salts and particularly by alkalis. Furthermore, coatings of the aforesaid compositions tend to undergo spot discoloration or undergo other chemical changes as a result of the metal ions anodically dissolved from the anode. Accordingly, there has been a desire to use coating compositions which will deposit at the cathode of an electrodeposition system.
A substantial number of binders are disclosed in the literature carrying groupings neutralizable with acids which can be deposited on cathodically wired objects of an electrodeposition system. Many have disadvantages primarily due to the need to have crosslinking additives in the coating compositions which adversely affect film characteristics. Recently, however, coating compositions have been provided which are self-crosslinking through thermal polymerization. These self-crosslinking binders include binders comprising:
(A) the reaction products of diepoxy compounds with alpha, beta-unsaturated acids and, optionally, long chain fatty acids, and basic monoisocyanates as described in copending application Ser. No. 816,936 filed June 19, 1977, now U.S. Pat. No. 4,238,594, assigned to the assignee of the present application;
(B) reaction products of diepoxy compounds with monoamines and, optionally, fatty acids, and unsaturated monoisocyanates as described in copending application Ser. No. 816,937 filed July 20, 1977, now U.S. Pat. No. 4,320,220, assigned to the assignee of the present application; and
(C) two moles of a diepoxy compound plus one mole of a primary-tertiary or secondary-secondary diamine plus two moles of an alpha,beta-unsaturated monocarboxylic acid and, optionally, an unsaturated fatty acid, plus an unsaturated monoisocyanate as described in copending application Ser. No. 849,265 filed Nov. 7, 1977, now U.S. Pat. No. 4,147,676, assigned to the assignee of the present application. The aforesaid binders are highly desirable due to their ability of self-crosslink through the presence of alpha,beta-unsaturation; their being water-soluble in the presence of acids due to the basic nitrogen atoms, and their ability to provide excellent films with good performance characteristics, particularly regarding resistance to corroding influences. The aforesaid binders, however, utilize expensive components and, accordingly, cannot be used for many applications because of cost.